Means for transferring power to and from magnetrons



J1me 1954 J. T. RANDALL ETAL 2,680,827

MEANS FOR TRANSFERRING POWER TO AND FROM MAGNETRONS Filed Sept. 4, 194:72 Sheets-Sheet l 'IIIIJIIII'IIIIIIIIA m %z'y HTTORNEY June 8, 1954 IJ.-T. RANDALL ET AL V 0,

MEANS FOR TRANSFERRING POWER TO AND FROM MAGNETRONS Filed Sept. 4, 19472 Sheets-Sheet 2 Patented June 8, 1954 ED STATES 2,680,827 PATET EFICEMEANS FOR TRANSFER/RING POWER TO. AND FROM' MAGNETRONS ApplicationSeptember 4, 1947,. Serial Nc..7.72,19.8. In Great, BritainDecember-17,. 1941,

Section 1, Public Law 690,, August 8,1946 Patent expires December 17;1961 2 Claims.

This invention relates to high frequency electrical oscillators and moreparticularly to means for extracting power from and/or excitingtheoscillating resonators of a magnetron. The magnetron tube to whichthe invention is preferably applied is of the type having an anode blockdefining a central cavity and a plurality of resonating cavities openinginto the central cavity. The cathode is positioned along the axis of thecentral cavity. The anode block is a cylindrical metal block having alarge axial central hole drilled therein thereby providing the centralcavity, and also having a plurality of smaller holes drilled near theside of the main cavity thus providing resonator cavities.

The prior art method of feeding oscillatoryenergy to and/or from suchmagnetron oscillators consists in the use of an electromagnetic couplingloop which forms one end of a concentric transmission line and isinserted in one of the resonators. At very short wave lengths (forexample, those of less than about five centimeters) the resonators areso small that this method becomes difiicult to apply. This invention hasas its primary object to feed energy to and/or from magnetronoscillators without the disadvantages of the aforementioned prior artmethod. The present invention is therefore particularly, but by no meansexclusively, applicable to apparatus operating on the very small wavelengths referred to. Other objects of the invention include theprovision of simpler and more satisfactory means of feeding energy toand/or from magnetrons than has been heretofore known.

Other objects and advantages of the invention will appear as thisdescription proceeds.

It is well known that a conducting tube will act as a wave guideprovided its diameter is equal to or greater than a critical valueproportional to the wave lengths employed; that is, oscillatory energyfed into the tube will be confined within, and transmitted along it withvery little loss. Accoding to the invention high frequency electricaloscillators of the type preferred to are characterized in that theresonator system is arranged to feed energy directly to and/or receiveit directly from such a Wave guide without the interposition of anyother type of transmission system.

According to a preferred arrangement an aperture is formed in one of thewalls of the magnetron for the purpose of allowing radiated energy topass from one of the resonator cavities to a, wave guide. The wave guideis arranged to form an electrically continuous surface with the 2 wallin which the aperture is formed in order to prevent any loss of radiatedenergy. Forthe purpose of maintaining a vacuum within the body of theoscillator it will in general be necessary to close the aperture by aseal of glass or other suitable non-conducting material, but if in anyparticular application it is convenient to maintain a vacuum in the waveguide itself n such a seal may, of course, be dispensed with. In oneconvenient arrangement the wave guide is adapted to fit over a smalllength of metal tube which is soldered or otherwise secured over theaperture and has a small glass dome or thimble sealed over its outerend.

In the complete specification accompanying copending application of JohnT. Randall and Henry A. H. Boot, Serial No. 407,680, filed August 20,1941, now U. S. Patent 2,542,966 granted February 20, 1951, anarrangement is described whereby power is fed to a wave guide from themagnetron through a concentric transmission line, a small aeriaconsisting of the free end of the central core of the transmission linebeing arranged to project within the wave guide. According to a furtherarrangement described in the said specification the free end of acoupling loop arranged within one of the resonators is formed into asimilar loop which is inserted within a wave guide. Neither of thesespecific arrangements falls within the scope of the present invention,since in the one case a concentric transmission line, and in the othercase the double-ended coupling loop (which forms in effeet the centralmember of a very short length of concentric transmission line) isinserted between the magnetron and the wave guide.

The invention, being generic, not only covers the specific form of ourinvention hriefiy mentioned above, but also other forms. In particularone of these other forms is characterized by small antennas attached tothe pole pieces of the magnetron thus establishing radiators which willdirect waves down a wave guide which faces said antennas. A reflectormay be provided to direct the Waves into the wave guide. The antennasmay be simple radiators attached to the pole pieces, or they may be thestraps of the so-called strap magnetron.

In the drawings:

Figure 1 is a longitudinal crosssection of a magnetron incorporatingthat form of my invention where antennas are connected to the polepieces for the purpose of directing the output into a wave guide.

Figure 2 is a sectional view along line 22 of Figure 1.

Figure 3 is a longitudinal cross-section of another form of theinvention and has an antenna for directing energy into a wave guide.

Figure 4 is a sectional view along line 4-4 of Figure 3.

Figure 5 is a longitudinal cross-section of a so-called strap magnetronembodying the invention.

Figure 6 is a sectional view taken along line 6-6 of Figure 5.

Figure 7 is a detailed view of the straps of a strap magnetron withcertain modifications to adapt the same for certain particularapplications in connection with this invention.

Figure 8 is a longitudinal cross-section of another form of thisinvention.

Figure 9 is a plan view showing certain details of the device of Figure8.

Figure 10 is a longitudinal cross-section of the preferred form of thisinvention and employs a direct opening from the wave guide into one ofthe resonator cavities for extracting high frequency energy therefrom.

While the invention is particularly applicable to magnetron oscillatorsadapted for generating large amounts of power and transmitting suchpower to a radio or radar transmitting antenna, the invention is alsoapplicable to radio receiving tubes of the magnetron type. Therefore,wherever in these specifications we refer to extracting energy from theresonator it is understood that the same structure may be used forexciting the magnetron with waves received from a radio receivingsystem.

Referring to Figures 1 and 2 there is shown a metal cylindrical block 29defining a central cavity 23 and eight smaller resonator cavities 24arranged about the central one and having slit openings thereinto. Anoxide-coated cathode '22 heated by filament 2! is concentric with theinner cavity 23. The block is located within a sealed evacuated glassenvelope 25, and leads 2% and 2'! pass into the envelope to energize thefilament 21.

At opposite ends of block 28 there are end spaces 28 and 29. Beyondthese end spaces and outside of the envelope are located the poles 3Gand 31 of a powerful magnet. Briefly speaking the mode of operation ofthe parts of Figures 1 and 2 thus far specifically described is that thecathode 22 emits electrons toward the positively charged anode block 20.Due to the strong cross-field of magnet 3B3l the electrons depart from aradial motion to a motion more nearly concentric to the pole pieces andas they graze the pole pieces and pass the slits leading to theresonators they set up oscillations in the resonators. Hence, currentsflow along the inner surfaces of the resonators charging alternatesegments with opposite polarities. These alternate polarities react onthe electron stream to cause the electrons to tend to bunch and byreason of the interaction of the resonators and the bunches of electronspassing each slit the oscillations are built up to a high degree in eachresonator cavity 24. Due to the interaction of the bunches of electrons(which affect all resonator cavities 2 3) with the currents circulatingin each cavity, a load may be placed upon all of the resonator cavitiesby extracting energy from any one of them. This fact together with acomplete statement of the basic theory of operation of the magnetron maybe found in the prior i copending application of James Sayers, SerialNo. 577,067, filed in the United States Patent Ofice February 9, 1945,now U. S. Patent- 2,5a6,8'2'0, granted March 27, 1951, as well as in theprior copending application of John T. Randall and Henry A. H. Bootabove referred to.

We have found that a load may be placed upon the whole system ofresonators by connecting two anode segments of opposite polarity to anelectrical loading circuit. In Figures 1 and 2 we connect radiators 32and 33 respectively to anode segments 34 and 35. Furthermore in these fiures the radiators 32 and 33 are respectively at opposite ends of theanode block 253. Since these radiators are connected to anode segments34 and 35 of opposite polarity they form an efficient radiator and thefield set up between them causes radiation to pass through the glassenvelope portion 3i and down the tuned wave guide 30. Some radiationwill of course be accomplished even though one of radiators 32 or 33 isomitted, and moreover some radiation will also take place if bothradiators 32 and 33 are connected to anode segments of similar polarity.

Referring to the modified form of Figures 3 and i, there is shown ananode block it defining a central cavity 32 together with a plurality ofresonator cavities 3 connected to the central cavity by slits operatingas heretofore described. A cathode t! is energized by current throughleads d6. A wave guide 38a is provided to transmit the energy away fromthe magnetron, and a sealing member 43 is employed to hold the glassseal 55: in proper position. Two radiators, which may also be termedantennas, ed and 5, are respectively connected to anode segments whichare of opposite polarity.

In Figures 5 and 6 we illustrate a so-called strap magnetron, thecathode being omitted, Like the magnetrons described above, the oneshown in Figure 5 has a cathode, a central cavity 5d, eight resonatorcavities 5i respectively having slits leading to the central cavity andan anode block 59 positively charged. A wave guide E i leads the energyfrom the system and the glass seal 15 maintains the cavities evacuated.The straps are circular conducting leads 53 and 54 (see Figure 6). Theconductor 53 connects to all the anode segments of one polarity,namelyanode segments 55, 55, 5? and 58. The conductor 5d connects to theremaining anode segments which are of course of opposite polarity tothose just mentioned, that is conductor 56 connects to pole pieces 53,5%, 6i and 52. Another similar system of straps is-preferably located atthe left end of the magnetron and is shown at '13. The principle ofoperation of the straps just mentioned is described in the copendingapplication of James Sayers already referred to. The straps 53 and 54 ofFigures 5 and 6 of this specification radiate energy into wave guide M.

For maximum efliciency the straps 53 and 54 should not be so large as toextend beyond the planes of the several surfaces of the wave guide. Inother words, the radiating electrodes should direct their radiationsinto the Wave guide and should therefore be smaller than and facing theopening in the wave guide. When the wave guide becomes so small thatthis is not possible, the radiators l9 and ii of Figure 'I may beemployed, to direct the energy into the wave guide Hi.

The modified form of the invention which is illustrated in Figures 8 and9 has an anode block defining a plurality of resonator cavities 8i allconnected by slits to the central cavity 82. The cathode 83 of the usualtype is provided, but in this case has an end shield 81 connected to thecathode and operating at cathode potential. One function of the endshield 81 is described in the said prior copending application of JamesSayers as preventing stray electrons from passing into the end spaces.In the present invention, the end shield 8! has the additional functionof acting as a reflector to direct the energy into the Wave guide 84through the glass seal 85. Preferably the reflector 81 should lieonequarter wave length behind the radiator 86 which may be any of theradiators already mentioned but is shown in Figures 8 and 9 as aplurality of wires forming radiator 85 of grid-like formation. Theradiator 86 is preferably connected to one or more voltage antinodes ofthe system. If connected to more than one, they should preferablycoincide in amplitude and phase. The radiator 86 lies in a plane atright angles to the axis of the wave guide 84 and therefore the energyis directed into the wave guide.

The preferred form of our invention is disclosed in Figure 10 wherein ananode block 93 is connected to the positive side of a high voltage powersupply. The cathode is connected to the negative side of such source andwires l0l energize the filament to heat the cathode. A central cavity 9|feeds a plurality of resonator cavities 92. The

magnetron of Figure 10 generates power in its resonators in the mannerhereinbefore described, and the power is extracted by a small hole 94 inone of the resonator cavities 92. In the usual constructions of theprior art a coupling loop system is inserted into one of the resonatorshalf way alon its length. Instead of this arrangement, however, the hole94 in the resonator system may be used as a radiating aperture. At wavelengths of the order of ten centimeters the aperture obviously cannot besuch as to act directly as a wave guide. The aperture 94 and wave guide96 may therefore be joined by a suitable metal cone 91, the vacuumenclosure being completed by the glass seal 95. Should a rectangularwave guide be 3 preferred a suitable adaptor can be provided, and theaxis of the resonator slot will be parallel to the long axis of the waveguide. Like in the case of all the magnetrons described herein, themagnetron must have magnetic flux in line with the axis of the centralcavity and in Figure 10 the magnet poles l 02 and I03 provide thedesired flux.

It is clear from the drawings that an advantage of our invention residesin the fact that the end of the wave guide is contiguous with the anodeblock. For example, in Figure 3, the wave guide 48a is anchored andsupported by the heavy anode block 40. Likewise in Figure 10, the waveguide 96 is attached directly to the anode block 93, re-

sulting in a simple, rigid and reliable arrangement.

We claim to have invented:

1. A magnetron comprising an anode block defining a main cavity and aplurality of cavity resonators opening into the main cavity, said anodeblock havin anode segments separating the cavity resonators from eachother, antennas respectively connected to anode segments of oppositepolarity and at opposite ends of the anode block, a magnet havingmagnetic flux along the axis of said main cavity, pole piecesrespectively adjacent opposite ends of the anode block, said antennasextendin from said anode segments in a direction generally perpendicularto the said magnetic fiux to a region beyond the side of the anodeblock, and a wave guide having its axis perpendicular to the path ofsaid flux and in the path of the field set up by said radiators.

2. A magnetron comprising an anode block (16- fining a centralcylindrical main cavity and a plurality of resonator cavities about andopening into the main cavity, a cathode extending alon the axis of themain cavity, magnet poles at opposite ends of the main cavity forestablishin a field through the block parallel to said axis, meansconnected to said block and associated with one of said resonatorcavities and extending away from that resonator cavity at substantiallyright angles to said axis for transferring electromagnetic energy fromthat resonator cavity away from said block in a direction perpendicularto that of the first-named axis, and a wave guide surrounding an outerportion of said means to thereby interchange energy with it, said meanscomprising a pair of antennas respectively directly connected toopposite ends of the anode block and respectively connected to the anodesegments at opposite sides of said one resonator cavity, said antennasextending generally perpendicular to the axis of the main cavity andinto the said wave guide.

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